Sharp LC-60LE847U

[ljintexas]

No standby, no power led. Dead. Several obervations. I have 120 volts at input plug, but as I check components from fuse on, all is 60 volts AC to chassis. Makes no difference if I unplug all connectors to other boards. When Testing R7002, which does not look like a resistor, I have 120 volts on one side and milivolts on the other side. Could this be a fuse? Also have three MOVs. One at main fuse measures 1.5 megohms..other two which are parallel downstream measure less than 1 ohm.
Next will check for standby voltage, 3.3 volts, 13 volts.

[ljintexas]

Re: Sharp LC-60LE847U

My apologies for not including pics!

Thanks

[ljintexas]

Re: Sharp LC-60LE847U

Performed reset by holding vol down and input keys while applying ac voltage. Green LED on main board blinking..after 5 min got two slow blinks followed by two fast blinks then two slow, two fast blinks of chevron V below Sharp on front panel.

[ljintexas]

Re: Sharp LC-60LE847U

Evidently, that indicates the lack of the 13.2 volts from smps which I verified on pins 5,6,7,8. Now to try and find the 13.2 volt section of the board. Any ideas?

Thanks

[gravesent]

Re: Sharp LC-60LE847U

I'll take a look and let you know what I find.

[gravesent]

Re: Sharp LC-60LE847U

So I have highlighted what I would check to make sure they're not dead shorts or low.

[ljintexas]

Re: Sharp LC-60LE847U

Pins 5,6,7,and 8 are all common to the center leg of D7130 which is the 3 leg FET

[ljintexas]

Re: Sharp LC-60LE847U

They are also common to the far right leg of Q7120, the 4 leg transistor is it?

[R_J]

Re: Sharp LC-60LE847U

I did find a bulletin on this power supply, It may help. or not. Also when measuring voltages in the primary or HOT side of the power supply, you don't use chassis ground as a reference, you need to have your ground probe on the hot ground, usually the large main capacitor (-)

[ljintexas]

Re: Sharp LC-60LE847U

It would seem the 4 leg regulator may be the issue..KIA378R12PI.
Vout is what is common to all of the 13 volt pins..measure Vin to Vout and I get 2.6 MegOhms..I think this may be a problem.

[budm]

Re: Sharp LC-60LE847U

What do you have on the Vin of that 12V LDO IC (KIA378R12PI), and the control pin?
What DCV do you have on the connector between the power supply board and the main board when power switch is not activated/activated.
Make sure to list the pin numbers and the pin names and follow by the DCV reading of each pin.
I.E.
Connector PD
Pin 1 (5VSTBY) = xx V.

https://www.badcaps.net/forum/showthread.php?t=49088

[ljintexas]

Re: Sharp LC-60LE847U

I had it pulled out of circuit, but put it back in circuit to check voltages.

will post results

Thanks Bud

[ljintexas]

Re: Sharp LC-60LE847U

All of the 13 volt pins are common to the Vin leg of the LDO IC. That would suggest that it is not GETTING 13 volts..there is a bank of 470 x 25 volt electrolytics next to it, of which some of are in circuit with the LDO. Hmmmmm

[budm]

Re: Sharp LC-60LE847U

Need to get good well focused pictures of the bottom side of the board so I can do the reverse engineering. More likely the SMPS is not running that is why there is no 13V at the input pins of the 12V LDO.

[ljintexas]

Re: Sharp LC-60LE847U

I checked D7805, it passed a diode test..so much for the TSB. I reinstalled the heat sink with both ICs and re-installed in TV. SMPS is running as I tested with main board connected and disconnected.. I now have my 13 volts to pins 5,6,7, and 8! maybe cold solder joint? Upon first fire up then I got 2 then five flashes which indicates:
DET_PNL12V (34pin) failure (L). Panel power is not
applied.
Detection is started after turning on the panel power and
receiving command; the power is turned off by polling.
Rebooted tv by cycling power..now no error codes but no display.
Thanks Bud! I appreciate your help!

[budm]

Re: Sharp LC-60LE847U

So do you have 12VDC at the output in of the 12V LDO?
Connector PD pin 1, 2 PNL_12V.
DPS-140TPA.
Pictures provided by SHOPJIMMY.

[ljintexas]

Re: Sharp LC-60LE847U

Yes, I do Bud. However there seems to be something going on as every few minutes I lose it for a short time then it comes back. Almost like something is shutting down then restarting. I also measured the FETs under the heatsink in the center of the board. When I have 12 volts on PD 1,2, I have 404 volts on the top FET in the center..when I lose the 12 volts, it goes down to 250 volts. When 12 volts comes back, I have 404 again.

[budm]

Re: Sharp LC-60LE847U

I am not sure which FET you are talking about and 404 Volts is way off to be that high without damaging the components.

[ljintexas]

Re: Sharp LC-60LE847U

Q7601 has 404 volts on the center leg.

[budm]

Re: Sharp LC-60LE847U

OK, the Power MOSFET Q7601 and the Q7602 (these two MOSFETs run off the 400VDC PFC Voltage booster circuit (Q7801) drive the power transformer T7601 which produces the Voltage for the LED driver circuit, it also produce the 13VUR.
So you may have bad solder joints on the board or PFC Boosted Voltage drops out. You should have about 400VDC measured between the two legs of either one of the two main filter caps C7800A/B.
You should also look at the DCV of the AC-DET pin to see if it drops down from 3VDC (normal condition should be >3VDC (HI)).
You should also retouch the solders on the transformer legs and the devices mounted on the heatsinks.